Nickel plating

ABSTRACT

AN ELECTROLYTE AND METHOD FOR ELECTROPHATING SEMIBRIGHT, SULFUR-FREE, NICKEL PLATE. THE ELECTROLYTE CONTAINS TWO COOPERATING ADDITIVES. ONE IS FROM THE GROUP CONSISTING OF FORMALDEHYDE, PARAFORMALDEHYDE, CHLORAL, CHLORAL HYDRATE, BROMAL AND BROMAL HYDRATE. THE SECOND IS A COMPOUND CONTAINING AN OXYOMEGASULFOYHYDROCARBON-DI-YL- COUMARIN ANION WHEREIN THE OXYOMEGASULFOHYDROCARBON-DI-YL GROUP IS SUBSTITUTED ON THE CARBOCYCLIC NUCLEUS OF THE COUMARIN GROUP.

United States Patent ABSTRACT OF THE DISCLOSURE An electrolyte andmethod for electroplating semibright, sulfur-free, nickel plate. Theelectrolyte contains two cooperating additives. One is from the groupconsisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate,bromal and bromal hydrate. The second is a compound containing anoxyomegasulfoyhydrocar- 'bon-di-yl coumarin anion wherein theoxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclicnucleus of the coumarin group.

As is well known to those skilled-in-the-art, nickel may beelectroplated onto various basis metals to obtain a bright nickelsurface. When it is desired to produce a nickel surface possessingmaxium brightness and luster and/or when the surface of the basis metalmay possess numerous scratches or other minor imperfections, it iscommon to electroplate onto the surface of a first layer of nickelparticularly characterized by its leveling ability. This deposit may becalled a semi-bright deposit because it does not possess the extermelyhigh brilliance and luster commonly attained by a bright-nickel deposit.There may commonly be deposited onto this first semibright nickel layera second bright nickel layer. The semibright nickel layer may bepolished and buffed prior to deposition of the bright nickel layer. Theresulting duplex-nickel system may be characterized by high degree ofbrilliance and by superior resistance to corrosion, even when the brightnickel deposit is relatively thin.

The first or semi-bright layer of nickel has heretofore commonly beendeposited from various nickel-plating baths, including for example Wattsbaths, sulfamate baths, chloride-free baths, etc., which contain anadditive. Prior art semi-bright nickel plating baths have commonly usedcoumarin as an additive. Although it may be possible to produce asemi-bright nickel deposit by prior art methods, there are numerousdefects which render these processes less than fully satisfactory.Semi-bright nickel deposits formed from plating baths of the prior artsuffer from inadequate leveling, high tensile stress and non uniformgrain size.

In an effort to correct these deficiencies of semi-bright nickel platingbaths, various additives have been used including coumarin derivativeshaving various groups attached to the aromatic or to the hetehocyclicring. These compounds have, however, been found not to be satisfactoryin that they do not permit attainment of an improved semi-bright nickelplate, but rather they have suffered from defects such as very lowsolubility, difficulty of synthesis, and tendency to readily decomposeduring electrolysis to give undesirable products, typically resinous orpolymeric materials which result in inferior deposits, etc.

It is an object of this invention to provide a novel process for theelectroplating of semi-bright nickel particularly characterized by itshigh leveling ability. A further object of the invention is to increasethe coverice age and luster in low current density areas, to increasetolerance to organic and metallic impurities, and to decrease thelikelihood of pitting over the entire area to be plated. Other objectswill be apparent to those skilledin-the-art on inspection of thefollowing description.

In accordance with certain of its aspects, the novel process of thisinvention for electroplating a semi-bright, sulfur-free, nickel pateonto a basis metal may comprise passing current from an anode to basismetal cathode through an aqueous acidic nickel plating solutioncontaining: at least one nickel compound providing nickel ions forelectroplating of nickel; a cooperating additive selected from the groupconsisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate,bromal, bromal hydrate; and including as a semi bright additive, acompound containing an oxyomegasulfohydrocarbon-di-yl coumarin anionwherein the hydrocarbondi-yl moiety contains at least two carbon atomsand wherein the oxyomegasulfohydrocarbon-di-yl group is substituted onthe carbocyclic nucleus of the coumarin group.

All nickel plating baths in commercial operation accumulate metallic(zinc, copper, etc.) and organic impurities (which may includedecomposition products of the coumarin derivatives). The cooperatingadditives of the invention reduce and minimize deleterious effects ofsuch impurities. For example, if some of the organic impurities tend togive coarsergrained, duller low current density deposits, thecooperating additives tend to counter-act these effects.

The basis metal onto which the semi-bright deposits of this bath may beapplied may include basis metals which are characterized by a low degreeof luster or brightness or which possess at degree of surface roughnesswhich would fail to permit attainment of a satisfactory quality of finalfinish and appearance if they were directly plated with a bright nickelplate. Typically the basis metals may include ferrous metals such assteel; copper, including its alloys such as brass, bronze, etc.; zinc,particularly in the form of die castings which may bear a plate ofcopper; etc.

The novel baths of this invention may typically include Watts-typebaths, sulfamate-type baths, ifluoboratetype baths, chloride-freesulfate baths, chloride-free sulfamate baths, etc.

A typical Watts bath which may be used in practice of this invention mayinclude the following components in aqueous solution, all values beingin grams per liter (g./l.) except for the pH.

TABLE I Minimum Maximum Preferred Component:

Nickel sulfate Nickel chlorid Boric acid-.. Semi-bright add pHeleetrometric i. 3 5

A typical sulfamate-type bath which may be used in practice of thisinvention may include the following components:

TABLE II A typical fluoborate-type bath which may be used in thepractice of the invention may include the following components:

A typical chloride-free-sulfate-type bath which may be used in practiceof this invention may include the following components:

TABLE IV Minimum Maximum Preferred Component:

Nickel sulfate 300 500 400 Boric acid 35 55 45 Semi-bright additive 0. 23 0. 75 pH electrometnc 3 5 4.

A typical chloride-free sulfarnate-type bath which may be used inpractice of this invention may include the following components:

TABLE V Minimum Maximum Preferred Component:

N iekel sulfamate 300 400 350 Boric acid 35 55 45 Semi-bright addltive0. 2 3 0. 75 pH electrometrie 3 5 4. 0

It will be apparent that the above baths may contain compounds inamounts falling outside the preferred minimum and maximum set forth, butmost satisfactory and economical operation may normally be effected whenthe compounds are present in the baths in the amounts indicated. Aparticular advantage of the chloride-free baths of Tables IV and V,supra, is that the deposits obtained may be substantially free oftensile stress.

The cooperating additives which may be used in the practice of thisinvention are selected from the group consisting of formaldehyde,paraformaldehyde, chloral, chloral hydrate, bromal, and bromal hydratein a nickel plating solution containing at least one nickel compoundproviding nickel ions for electroplating nickel. Preferred cooperatingadditives may be formaldehyde, paraformaldehyde, and chloral hydrate.

Only an amount of cooperating additive sufiicient to provide improvedplating characteristics for the nickel plating solution containing atleast one nickel compound providing nickel ions for electroplatingnickel is necessary. Typically amounts of cooperating additives of fromabout 0005-110 g./l., such as 0.05-0.5 g./l. and preferably 0.08-0.30g./l. may be used in the invention. The cooperating additives may beused in combination with each other and in such case the amount ofcooperating primary additives refers to the total amount of suchadditives.

The semi-bright additives which may be employed in practice of thisinvention according to certain of its aspects may include compoundscontaining the oxyomegasulfohydrocarbon-di-yl coumarin anion wherein thehydrocarbon moiety contains at least two carbon atoms. Theoxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclicring of the coumarin nucleus. The hydrocarbon-di-yl moiety may bearinert substituents. Typically such compounds may include those whereinthe cation M (see infra may be a bath-compatible cation, i.e. a cationwhich is soluble in the electroplating bath and which does not interferewith attainment of the desired semi-bright plate. Typically, the cationM may include hydrogen and alkali metals including sodium, potassium,lithium, etc.; polyvalent metals such as nickel,

cobalt, magnesium, etc. The omega carbon atom of these novel compoundsis the carbon atom linking the sulfo group to the remainder of themolecule. Most commonly the omega position is the carbon atom mostdistant from the coumarin nucleus. However, when a hydrocarbondi-ylgroup in the chain linking the coumarin nucleus to the sulfo groupcontains carbon-containing substituents, the omega position as hereindefined may not be the carbon atom most distant from the cournarinnucleus.

When the cooperating additives are used in cooperation with the coumarinderivatives, besides increasing the general deposit luster anduniformity and acting as anti-pitters and low current density coverageand luster promoters, they also act as extenders, i.e. since they aregood grain refiners they still perform one of the functions of thecoumarin derivatives and since they are relatively inexpensive incomparison with the latter they permit lower cost operation.

The novel compounds containing the oxyomegasulfohydrocarbon-di-ylcoumarin anion may typically have the following formula:

wherein a, b c and d are each integers less than two, i.e. o and l, thesum of a, b, c, and d being greater than 0 and preferably 1 and whereinM is a cation as defined supra, R is a hydrocarbon-di-yl group whereinthe hydrocarbon moiety contains at least two carbon atoms, and X is aninert substituent. Typical inert substituents (i.e. substituents whichdo not cause unfavorable eifects to occur in electroplating bathsincluding the novel compounds of this invention), include hydrogen,halagen, e.g. chloro, alkyl, alkaryl, aralkyl, aryl, alkoxy, aryloxy,etc. As shown, the inert substituent when present is preferably on thearomatic ring of the coumarin nucleus.

In the above formula R may be a divalent hydrocarbon group having atleast two carbon atoms. Typically R may be arylene such as o-phenylene;m-phenylene; pphenylene; aralkylene such as o-benzyl; m-benzyl; orpbenzyl; alkarylene such as 1-methyl-2,3-phenylene; 1- methyl 2,4phenylene; 1-methyl-2,S-phenylene; etc., alkylene such asethane-1,2-di-yl; propane-1,2-di-yl; propane-1,3-di-yl;butane-1,4-di-yl; butane-1,3-di-yl; pentane- 1,5-di-yl; etc. Thesegroups may bear inert substituents including hydrocarbon substituents.The preferred R group may contain at least three carbon atoms, and morepreferably 3-5 carbon atoms in a straight chain extending from thecarbon atom closest to the coumarin nucleus to the omega carbon atom,the omega position being as hereinbefore defined. Preferred R groups maycontain a linked chain of methylene groups and the most preferred R maybe propane-1,3-di-yl, CH CH CH In formulae containing a plurality of Rgroups, the R groups may preferably be the same.

With respect to Formula I supra, it will be apparent that when a is l, bis 1, c is 0, and d is 0 the formula may be:

and that when a is O, b is 1, c is 1, and d is the formula may be:

. X (III) and that when a is 0, b is l, c is 0, and d is O the formulamay be:

It will be apparent that the values of a, b, c, and d may beindependently varied between 0 and 1 to produce coumarin derivativesother than those specifically set forth.

It will also be apparent that when M is polyvalent, the valences thereofmay be satisfied by linkage to other oxyomegasulfohydrocarbon-di-ylgroups which may be on the same or on another coumarin nucleus. Forexample, when M is divalent, e.g. nickel, the compound may have one ofthe following illustrative formulae, inter alia:

The preferred compounds may include those having Formula IV wherein theoxyomegasulfohydrocarbon-di-yl group is substituted on the 7-position ofthe coumarin and M is an alkali metal; also preferred are thosecompounds wherein R is 'a hydrocarbon-di-yl group having 3-5 carbonatoms and most preferably one wherein R is a polymethylene chainpreferably having 3 carbon atoms, viz:

wherein n is preferably 35, and most preferably 3.

It will be apparent to those skilled-in-the-art that the compounds notedsupra will provide the baths of this invention with the desired anionviz:

or the following corresponding anions to the above-noted specificcompounds, (II), (III), and (IV):

Typical preferred specific compounds Which may be used in practice ofthis invention may include:

TABLE VI potassium 7-oxyomegasulfopropyl coumarin potassium6-chloro-7-oxyomegasulfopropy1 coumarin sodium 7-oxyomegasulfopropylcoumarin sodium 6-chloro-7-oxyomegasulfopropyl coumarin disodium6,7-di(oxyomegasulfopropyl) coumarin disodium7,8-di(oxyomegasulfopropyl) coumarin nickel 6,7-di(oxyomegasulfopropyl)coumarin cobalt 7,8-di(oxyomegasulfopropyl) coumarin nickeldi(7,7'-oxyomegasulfopropyl) coumarin potassium (8-oxyornegasulfopropyl)coumarin potassium (6-oxyomegasulfopropyl) coumarin sodium5-oxyomegasulfobutyl coumarin potassium 7-oxyomegasulfobutyl coumarinsodium 7-oxyomegasulfobenzyl coumarin (i.e. sodium 7-oXy-orthosulfobenzyl coumarin), viz.:

The most preferred compounds may typically be the first four compoundsin table VI. It will be apparent that other cations as hereinbeforenoted may replace those present in the specific compounds in Table VI.

The novel oxyomegasulfohydrocarbon-di-yl coumarin compounds, wherein thehydrocarbon-di-yl moiety contains at least 2 carbon atoms and theoxyomegasulfohydrocarbon-di-yl is substituted on the carbocyclic nucleusof the coumarin group of this invention may, in accordance with certainof its aspects, be prepared by the process which comprises mixing in asolvent dispersion, a hydroxy coumarin wherein the hydroxy group issubstituted on the carbocyclic nucleus of the coumarin group, a compoundof the formula MOH wherein M is a cation including those hereinbeforenoted, and a hydrocarbon sultone wherein the hydrocarbon moiety containsat least 2 carbon atoms thereby forming a reaction mixture, and heatingsaid reaction mixture.

The solvents used in this preparation may preferably be those in whichthe reactants are dispersible, i.e. suspendable or soluble and mostpreferably one in which the compound MOH is soluble. Such solvents maytypically include organic solvents such as alcohols, etc.

The sultones which may be employed to prepare the novel compounds ofthis invention may include those containing acarbon-oxygen-sulfur-carbon linkage in a ring, the hexavalent sulfuratom being further bonded to two additional oxygen atoms. The sultonewhich may preferably be used may contain 3-5 carbon atoms, thesesultones being characterized by generation of a minimum of foaming. Themost preferred sultone may be 1,3-propane sultone,

although sultones such as 1,4-butane sultone,

CH2 Cg GH CH2 S 62 and 1,3-butane sultone,

HCH

(IJHZ S 62 also may produce highly useful additives. The longer chainalkane sultones or other sultones containing more than 5 carbon atoms,such as tolyl sultone,

may also be used to produce additives within the scope of the invention.

Hydroxy-coumarins which may be used in preparing the novel compounds mayinclude the following hydroxy coumarins which carry one hydroxylsubstituent on the carbocyclic nucleus of coumarin, typically includingmonoand poly-hydroxy coumarins such as:

S-hydroxy coumarin 6-hydroxy coumarin 7-hydroxy coumarin 8-hydroxycoumarin 6,7-dihydroxy coumarin 7,8-dihydroxy coumarin6-chloro-7-hydroxy coumarin Preferred coumarins may include the7-hydroxy coumarins such as 7-hydroxy coumarin se.

These hydroxy coumarins may be readily available or may be prepared bythe reaction of the corresponding resorcinol with malic acid in thepresence of catalyst, e.g. concentrated sulfuric acid; e.g. to prepare6-chloro-7- hydroxy coumarin, malic acid may be reacted with 4-chlororesorcinol. Besides concentrated sulfuric acid other catalysts may beused such as the pyrophosphates of titanium and zirconium used singly orin combination.

The preferred compounds MOH which may be used in the process of thisinvention include alkali metal hydroxides such as sodium hydroxide,potassium hydroxide, and lithium hydroxide.

In a preferred embodiment of the invention, 2.3-3.3 parts, say 2.8 partsof MOH, preferably potassium hydroxide, may be added to 3-4 moles, say3.1 moles of solvent, preferably methanol. 7.5-11 parts, preferably 8.1parts of 5-, 6-, 7- or S-hydroxy coumarin, preferably 7-hydroxycoumarin, may then be added together with 4.9-7.3 parts, say 6.7 partsof hydrocarbon sultone, preferably 1,3-propane sultone. Preferably themolar ratio of MOH to hydrocarbon sultone may be about 1 to l. Thereaction mixture may then preferably be heated typically to refluxtemperature for 1-4 hours, say 2 hours. All parts referred to above areparts by weight.

At the conclusion of the reaction time, the reaction vessel may becooled and the desired product may precipitate. The product may beseparated, Washed with a solvent in which the product is sparinglysoluble, such as methanol and dried. Typically the pure yield may be atleast about 60% by weight based on the coumarin starting material,although crude yield may also be used as semi-bright additives toelectroplating baths without deleterious results. Alternatively, thesolvent, such as methanol, may be removed by heating under reducedpressure and the residual product dissolved in water to a convenientconcentration and used as the additive stock solution to essentiallyobtain a quantitative yield of the active ingredient.

If it be desired to convert the alkali metal salt of theoxyomegasulfohydrocarbon-di-yl coumarin to other salts, the alkali metalsalt of the oxyomegasulfohydrocarbondi-yl coumarin compound maypreferably be reacted with a cationic exchange resin such as a sulfonicacid cationic exchange resin on the hydrogen cycle. The free sulfonicacid in the eluate may then be reacted with the oxide, hydroxide,carbonate, etc., of the metal desired, e.g. nickel or cobalt toneutrality to form the desired metal salt of the free sulfonic acid. Anyexcess of the oxide, hydroxide, carbonate, etc., may be removed byfiltration.

The semi-bright oxyomegasulfohydrocarbon-di-yl coumarin moiety whereinthe hydrocarbon-di-yl moiety contains at least two carbon atoms andwherein the oxyomegasulfohydrocarbon-di-yl group is substituted on thecarbocyclic nucleus of the coumarin group may preferably be used innickel plating baths such as those of Tables I-V, in amounts of at least0.2 g./l. of plating bath. Lower concentrations may give appreciablegrain refinement but the deposits may be less glossy. When theconcentration of the oxyomegasulfohydrocarbon-diyl compound or groupexceeds 3 g./l. of plating bath, the results obtained generally do notprovide additional advantages over the lower ranges. The preferredconcentration ranges from about 0.5-1 g./l. of additive in the platingbath.

The presence of the cooperating additives of this invention in a nickelplating solution in combination with an oxyomegasulfohydrocarbon-di-ylgroup in the plating baths which may be used in this invention may befound to impart improved surface active anti-pitting properties and suchcombinations extend and augment the grain refining eifects of thecoumarin group, especially in low current density areas. The platingbaths may in addition contain optional additional constituents such asanionic Wetting agents which may be used to further reduce pittingeifects. High foaming anionic wetting agents such as sodium laurylsulfate may be used in conjunction with mechanical agitation; and lowfoaming anionic wetting agents such as sodium dialkyl sulfosuccinatesmay be used with air agitation. Although these wetting agents maycommonly contain sulfur, it has unexpectedly been found that no increasein the sulfur content of the metal deposits may be observed when thesewetting agents are used with the semi-bright additives and cooperatingadditives of the invention.

It is a particular feature of this invention according to certain of itsaspects that medium or very high-speed electroplating of semi-brightnickel may be eifected by the process comprising passing current from asubstantially non-polarizing anode to a basis metal cathode through anaqueous nickel plating solution including at least one nickel compoundcapable of providing nickel ions for electroplating nickel; acooperating additive selected from the group consisting of formaldehyde,paraformaldehyde, chloral, chloral hydrate, bromal, bromal hydrate insaid nickel plating solution; and including as a semibright additive acompound containing oxyomegasulfohydrocarbon-di-yl coumarin anionwherein the hydrocarbon moiety contains at least two carbon atoms andthe oxyomegasulfohydrocarbon-di-yl group is substituted on thecarbocyclic nucleus of the coumarin group, maintaining the cathodecurrent density during said plating at a level of at least amperes persquare decimeter (ASD) and maintaining a high relative velocity betweensaid nickel plating solution and said basis metal cathode therebyobtaining a glossy, leveled, semi-bright high-speed nickel plate withgood low current density coverage and reduced pitting.

The substantially non-polarizing anodes which may be used in the mediumor very high-speed electroplating aspect of this invention may beinsoluble anodes, such as lead which have very little tendency topolarize, even at very high current density, or certain soluble anodes,such as the commercially available SD type of nickel which has lesstendency to polarize than other soluble nickel anodes and may be used atcurrent densities as high as 40 ASD. The SD type of nickel is anelectrolytic nickel containing a controlled amount of sulfur.

Thus, according to this aspect of the invention a current density ofover about 10 ASD, and preferably of -60 ASD, may be used, although acurrent even as high as or higher than 120 ASD may be applied duringelectroplating of nickel using baths containing the novel additives ofthe invention. Plating carried out in this manner may permit depositionof predetermined thicknesses of semi-bright, leveled nickel in a timewhich is as little as 10% or less of the time required when ordinarilyused plating conditions with soluble nickel anodes are used. Typicallyproduction of a semi-bright nickel plate microns thick according to thisaspect of the invention may require 3 minutes in contrast to minutes forusual plating conditions.

When medium or very high speed electroplating is desired, a highrelative velocity may be maintained between the bath and the cathode-toattain a substantially homogeneous catholyte. This serves to replenishthe cathode fihn with nickel ions as they are plated out therefrom.Typically the high relative velocity between the bath and the cathodeis-maintained at a level equivalent to 60-320, say 150 cm./second. Theagitation may be produced by vibration (including ultrasonic), rotationof the cathode relative to the solution, by pumping the electrolyte,e.g. catholyte, through the system and over the cathode relative to thesolution, by pumping the electrolyte with appropriately positionedpropellers or other devices, etc.

Semi-bright nickel plating in accordance with this invention may also becarried out under lower speed conditions by immersing a basis metalcathode into a nickel plating bath as hereinbefore disclosed. The anodemay be either a soluble anode, typically nickel metal, or an insolubleanode, typically lead.

If nickel is used as the anode, it is preferably SD type of nickel andplating may be carried out in chloridecontaining baths for 30-60minutes, say 30 minutes at 4060 0, say '50 C., with mechanical or airagitation.

The current density may typically be 2.5-5 ASD, preferably 5 ASD;

The novel process of this invention may permit attainment of a 12.5 to50 microns, say 25 microns of semibright nickel plate characterized byits fine grain, high ductility, high gloss, uniform appearance, highleveling, and high covering power. The plate is also characterized byits essentially sulfur-free character.

The following illustrative examples disclose synthesis of typicaladditives of this invention, nickel plating baths containing the noveladditives of this invention, and electroplatng processes wherein thesebaths are used.

EXAMPLE 1 100 ml. of methanol, 2.8 grams of potassium hydroxide and 8.1grams of 7-hydroxy coumarin may be introduced into a 500 ml. Erlenmeyerflask, to form a solution. 6.7

10 grams of 1,3 -propane sultone may then be added and the flask thenheated under reflux on a hot plate for 2 hours while the composition ismagnetically stirred. The solution may be cooled to ambienttemperatures, the precipitate obtained may be filtered out and thenwashed several times with methanol. The precipitate may then be driedfor 2 hours at 60 C., leaving 9.4 grams (59% 'yield) of potassium7-oxyomegasulfopropyl coumarin.

The melting point of 237 C.240 C. may then be determined.

EXAMPLE 2 6.5 grams of potassium hydroxide dissolved in ml. of methanolmay be introduced into a suspension of 20 grams of 6-chloro-7-hydroxycoumarin in 300 ml. of methanol producing a precipitate. The suspensionmay then be heated to reflux and a solution of 13 grams of 1,3-propanesultone in 100 ml. of methanol added drop- 'wise over a 15-minuteperiod. This may be followed by stirring and refluxing for 4 hours toobtain a precipitate of potassium 6-chloro-7-oxyomegasulfopropylcoumarin. The methanol may be removed by heating in a stream of air,leaving 40 grams of the crude coumarin derivative. The compound does notmelt at temperatures of up to 300 C.

EXAMPLE 3 Other coumarin derivatives which may be prepared according tothe general methods of the above examples include sodium7-oxyomegasulfopropyl coumarin, prepared in a methanol solventinteraction of 7-hydroxy coumarin, 1,3-propane sultone and sodiumhydroxide.

EXAMPLE 4 1 liter of the following Watts bath may be prepared:

Nickel sulfate: 300 g./l. Nickel chloride: 60 g./l. Boric acid: 45 g./l.

pH electrometric: 4.0 Water to 1 liter.

The bath may be thermostatically controlled at 60 C. and air agitatedwith a perforated glass-plastic air agitation coil. A single cottoncloth bagged SD nickel anode may be positioned in the bath. A highlypolished brass strip of 20 cm. x 2.5 cm. x 0.08 cm., pleated in 45angles, may then be cleaned and immersed as the cathode in the bathexcept for the top 2.5 cm.

In a control run, a current of 2.5 amperes may be passed through thebath at 50 C. for 30 minutes to obtain a dull, grainy, non-uniformdeposit.

In practice of the invention, 0.8 gram of potassium 7-oxyomegasulfopropyl coumarin semi-bright additive and 0.1 gram offormaldehyde cooperating additive may then be mixed into the bath andthe plating test repeated. This time a beautifully -fine grained, veryductile deposite of high gloss and very uniform appearance charterizedby excellent low current density coverage and relative freedom frompitting may be obtained. When a similar cathode, which had been scribedwith a single pass of 1.2 cm. wide zero-grit emery paper, was thereafterplated for 30 minutes using the bath containing the cooperatingadditives, the emery paper scratches may be found to be substantiallyfilled in, indicating excellent leveling at low current density areas.

EXAMPLE 5 4 liters of the Watts bath of Example 4 may be prepared and3.2 grams of potassium 7-oxyomegasulfopropyl coumarin and 0.5 gram ofthe low-foaming wetting agent sodium di-n-hexylsulfosuccinate addedthereto. Electroplating may be carried out using a bagged SD nickelanode; and a highly polished, brass cathode strip pleated in 45 anglesmay then be plated at a current of 5 amperes at 50 C. for 30 minutes toobtain a beautifully fine grained, very ductile deposit of high glossand very uniform appearance.

In practice of the invention, 0.1 gram of paraformaldehyde cooperatingadditive may then be mixed into the bath and the plating test repeated.This time a beautifully fine grained, very ductile deposit of high glossand very uniform appearance further characterized by excellent lowcurrent density coverage and relative freedom from pits may be obtained,indicating a substantial improvement due to the use of the cooperatingadditive.

The essentially sulfur-free character of the deposits may be determinedby analyzing the deposits obtained in Examples 4 and 5. It may be foundin each instance that the sulfur content is about 0.003% by weight. Thisvalue is so unusually low that the deposits may be considered to beessentially sulfur-free.

The beneficial characteristics exemplified by Examples 4 and 5 may bemaintained over prolonged periods of electrolysis, for example up to 500ampere-hours or longer by periodically adjusting the bath pH to withinrecommended limits as with dilute sulfuric acid and by replenishing theadditives.

EXAMPLE 6 1 liter of the following sulfamide bath formulation may beprepared:

Nickel sulfamate: 360 g./l. Nickel chloride: g./l. Boric acid: 45 g./l.

pH electrometric: 3.5 Water to 1 liter.

The process of Example 4 may be repeated using the same cooperatingadditives with essentially the same results obtained.

EXAMPLE 7 The process of Example 4 using the Watts bath thereof may berepeated using as the additive 0.8 gram of potassium 6 chloro 7oxyomegasulfopropyl coumarin as semi-bright additive and 0.1 g./l. ofchloral hydrate as cooperating additive with essentially the sameresults obtained.

EXAMPLE 8 EXAMPLE 9 4 liters of the following chlo'ride-free-nickel bathformulation may be prepared:

Nickel sulfate: 375 g./l. Boric acid: 45 g./l.

pH electrometric: 4.0 Water to 1 liter.

The bath may be thermostatically controlled at 70 C. and mechanicallyagitated by propellers during plating.

To this bath may be added 0.4 g./l. of potassium 6-chloro-7-oxyomegasulfopropyl coumarin and 0.05 g./l. of

chloral hydrate and 0.05 g./l. of formaldehyde. A single cotton clothbag SD nickel anode is positioned in the bath. A highly polished brassstrip cathode of 2.5 cm. x 20 cm. x 0.08 cm. may be scribed with asinglepass' of 1.2 cmywide zero-grit emery board. This strip may beclamped in a plastic fixture exposing only the scribed side of the stripto the anode and the plating bath discharged from a pressure pump toimpinge on the exposed scribed area of the strip at an'angle'of about A-current density of 40 amperes per square decimeter may be applied at C.for 3 minutes to obtain by this high speed process a glossy beautifullyfine grained, very ductile deposithaving a thickness of about 25 micronsand further char acterized by virtual freedom from pits. The cathodeplate attained from the chloride-free bath of this example possessesvery little tensile stress. The emery paper scratches theextent of0.005l.0 g./ 1. of the solution. a

may be found to be; substantially filled in and the-leveling isexcellent. 1

EXAMPLE 10 11 ence to specific examples, numerous changes andmodifications thereof. which clearly fall within the scope of theinvention. will be apparent to those skilled in the art.

I claim: p 1. A process of electroplating a semi-bright, sulfurfree,nickel plate onto a basis metal which comprises passing current from ananode to a basis metal cathode through an aqueous acidic nickel platingsolution containing at least one nickel compound providing nickel ionsfor electroplating nickel; and, in an amount sufficient to provideimproved plating characteristics, a cooperating additive selected fromthe group consisting of formaldehyde, paraformaldehyde, chloral, chloralhydrate, bromal, bromal hydrate and a compound containing anomegasulfohydrocarbon-di-yl coumarin anion wherein the hydrocarbon-di-ylmoiety contains at least two carbon atoms and wherein theoxyomegasulfohydrocarbon-di-yl groups is substituted on the carbocyclicnucleus of the coumarin group.

2. The process of claim 1 wherein the cooperating additive isformaldehyde.

3. The process of claim 1 wherein the. cooperating ad ditive is chloralhydrate or chloral.

4. Theprocess of claim 1 wherein the cooperating additive is bromalhydrate or bromal.

5. The process of claim 1 wherein the cooperating additive isparaformaldehyde. v I

6. The process of claim 1 wherein saidisemi-brightad, ditive is g A,Xi-iiM-OSb2.li.-O]a wherein X'is an inert substituent, M is a cation, Ris a hydrocarbon-di-yl group containing at least two carbon atoms, anda, b, c, and d are each integers less than 2,

the sum of a, b, c, and dbeing atleast 1.

7. The. process of claim 1 wherein said semi-bright additive is whereinM is a cation and-X is an inert substituent.

8. The process of claim 1 wherein said semi-bright additive is presentto the extent of at least about 0.2 g./l. of the solution and thecooperating additive is present to A process of electroplating asemi-bright nickel deposit which comprises passing current fromasubsta'n' tially non-polarizing anode to a basis metal cathode throughan aqueous acidicnickel plating solution includ- 1 ing at leastone-metal compound capable of providing" drate, bromal, bromal hydrateand 'a compoundc'oirtain ing oxyomegasulfohydrocarbon-di-yl coumarinwherein the hydrocarbon moiety contains at least two carbon atoms andthe oxyomegasulfohydrocarbon-di-yl group is substituted on thecarbocyclic nucleus of the coumarin group; maintaining the cathodecurrent density during said plating at a level of at least ten amperesper square decimeter, and maintaining a high relative velocity betweensaid chloride-free nickel plating solution and said basis metal cathodethereby obtaining a glossy leveled, semi-bright high speed nickel platecharacterized by good low current density coverage and substantialfreedom from pits.

10. A nickel plating solution comprising an acidic aqueous nickelplating solution including: at least one nickel compound capable ofproviding nickel ions for electrodeposition of nickel on a basis metalcathode; and in an amount sufficient to provide improved platingcharacteristics, a cooperating additive selected from the groupconsisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate,bromal, and bromal hydrate; and a compound containing anoxyomegasulfohydrocarbon-di-yl coumarin ion wherein the hydrocarbonmoiety contains at least two carbon atoms and theoxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclicnucleus of the coumarin group.

11. The nickel plating solution of claim wherein the cooperatingadditive is formaldehyde.

12. The nickel plating solution of claim 10 wherein the cooperatingadditive is chloral hydrate or chloral.

13. The nickel plating solution of claim 10 wherein the cooperatingadditive is bromal hydrate or bromal.

14. The nickel plating solution of claim 10 wherein the cooperatingadditive is paraformaldehyde.

15. The nickel plating solution of claim 10 wherein the semi-brightadditive is wherein X is an inert substituent, M is a cation, R is ahydrocarbon-di-yl group containing at least two carbon atoms, and a, b,c, and a are each integers less than 2, the sum of a, b, c, and d beingat least 1.

16. The nickel plating solution of claim 10 wherein said semi-brightadditive is wherein M is a cation and X is an inert substituent.

17. The nickel plating solution of claim 10 wherein said semi-brightadditive is MO-SOz(CH2)3O =0 wherein M is a cation.

18. The nickel plating solution of claim 10 wherein said semi-brightadditive is wherein M is a cation.

19. The nickel plating solution of claim 10 wherein said aqueous acidicnickel plating solution is chloride-free.

20. The nickel plating solution of claim 10 wherein said semi-brightadditive is present to the extent at least about 0.2 g./l. of thesolution and wherein said cooperating additive is present in an amountof 0005-10 g./l. of the solution.

References Cited G. L. KAPLAN, Primary Examiner UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION patent 3 ,556 ,959 Dated January 191971 Inventor(s) Frank 211 It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading to the printed specification, after line 4, insertassignor to MGT Chemicals Inc., New York, N. Y. a corporation ofDelaware Signed and sealed this 15th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR

Attesting Officer Commissioner of Patents

